1. Field of the Invention
The present invention relates to a water jet propulsion watercraft.
2. Description of the Related Art
A water jet propulsion watercraft travels on water by a propulsive force generated by a jet propulsion device attached to a hull. The jet propulsion device sucks in and jets water to generate the propulsive force.
For example, a water jet propulsion watercraft according to a prior art disclosed in U.S. Pat. No. 6,875,064 B2 includes a pair of right and left jet propulsion devices disposed at a rear end of a hull. In this prior art, the pair of right and left jet propulsion devices respectively include stator nozzles 301R and 301L, steering nozzles 302R and 302L, and reverse gates 303R and 303L as shown in FIG. 28. Each of the stator nozzles 301R and 301L discharges a water flow, generated by rotation of an impeller, toward a rear of the hull. The steering nozzles 302R and 302L are rotatable to right and left about pivot axes 304R and 304L. By the steering nozzles 302R and 302L rotating to the right and left, the directions of the water flows from the stator nozzles 301R and 301L are changed to the right and left. The direction of the water jet propulsion watercraft is thereby changed.
When the water jet propulsion watercraft is to be driven in reverse, the reverse gates 303R and 303L are disposed at the rear of the steering nozzles 302R and 302L. The reverse gates 303R and 303L respectively include first scoops 306R and 306L and second scoops 307R and 307L. The first scoops 306R and 306L are disposed comparatively far from a hull centerline 305 of the water jet propulsion watercraft. The second scoops 307R and 307L are disposed closer to the centerline 305 than the first scoops 306R and 306L.
The first scoops 306R and 306L direct the water from the steering nozzles 302R and 302L diagonally to the front of the water jet propulsion watercraft. The second scoops 307R and 307L direct the water from the steering nozzles 302R and 302L toward the centerline 305 of the water jet propulsion watercraft.
To drive the water jet propulsion watercraft straightly in reverse, the steering nozzles 302R and 302L are set straight with respect to the hull (in directions parallel to the centerline 305). In this state, the water jetted from the steering nozzles 302R and 302L flows outside the reverse gates 303R and 303L through the first scoops 306R and 306L or the second scoops 307R and 307L.
In this state, a water flow F301 discharged from the first scoop 306R is directed to the right front. The water flow F301 applies a left rearward propulsive force to the hull. A water flow F302 discharged from the second scoop 307R is directed substantially directly to the left. The water flow F302 applies a substantially directly rightward propulsive force to the hull. Likewise, a water flow F304 discharged from the first scoop 306L is directed to the left front. The water flow F304 applies a right rearward propulsive force to the hull. A water flow F303 discharged from the second scoop 307L is directed substantially directly to the right. The water flow F303 applies a substantially directly leftward propulsive force to the hull. A resultant vector of the forces applied to the hull by the water flows F301 to F304 is directed substantially directly rearward. A heading direction of the water jet propulsion watercraft is thus a directly rear direction D306.
On the other hand, to drive the water jet propulsion watercraft in reverse to the left, the steering nozzles 302R and 302L are directed to the right as shown in FIG. 29. In this case, the water from the right steering nozzle 301R flows outside the right reverse gate 303R through the first scoop 306R of the right reverse gate 303R. The water from the left steering nozzle 301L flows outside the left reverse gate 303L through the second scoop 307L of the left reverse gate 303L.
In this state, a water flow F307 discharged from the first scoop 306R is directed to the right front. The water flow F307 applies a left rearward propulsive force to the hull. A water flow F308 discharged from the second scoop 307L is directed to the right rear. The water flow F308 applies a left frontward propulsive force to the hull. A resultant force of the propulsive forces generated by the water flows F307 and F308 is directed left rearward. Thus, theoretically, the heading direction of the water jet propulsion watercraft is a left rear direction D310.
To drive the water jet propulsion watercraft in reverse to the right, the steering nozzles 302R and 302L are rotated to the left and theoretically, the water jet propulsion watercraft is thereby driven in reverse in a right rear direction in a manner similar to that described above.